Process for producing multi-coat system on substrate

ABSTRACT

The present invention relates to a process for producing a multi-coat system on various substrates, particularly automotive bodies. A crosslinkable component of the composition includes an acid functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of one or more carboxylic acid group containing monomers, percentages based on total weight of the acid functional acrylic copolymer, and 0.2 percent to 2 percent of amorphous silica, percentages based on total weight of the crosslinkable component. The crosslinking component can includes polyisocyanates, melamines, or a combination thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to curable compositions and moreparticularly relates to low VOC (volatile organic component) ambienttemperature curable coating compositions suitable for use in automotiveOEM (original equipment manufacturer) and refinish applications.

2. Description of Related Art

A number of clear and pigmented coating compositions are utilized invarious coatings, such as, for example, primer coats, basecoats andclearcoats used in automotive coatings, which are generally solventbased.

Multi-coat systems were developed to satisfy a need for improvedaesthetics of the coated substrate. A multi-coat systems typicallyinclude a primer coat, followed by a basecoat, which is typicallypigmented and then finally a clearcoat that imparts a glossy appearanceof depth that has commonly been called “the wet look”.

In a multi-coat system it is necessary that a basecoat have “strike-in”resistance. By “strike-in” resistance is meant the ability of a basecoatlayer of a pigmented coating composition to resist attack by thesolvents in a layer of a clear coating composition applied over thebasecoat layer thereby preventing any change in the color of a pigmentedbasecoat. The strike-in is a problem because the automobilemanufacturers generally wish to apply the clear coating composition by a“wet-on-wet” technique. By this is meant that a basecoat layer of apigmented composition is applied to a substrate. Then after flashing thebasecoat layer a topcoat layer of a clear composition is appliedfollowed by a single curing step utilized to cure the multi-layersystem. The “striking in” of the topcoat layer into the basecoat layeris particularly undesirable since it adversely affects alignment, i.e.,flop, of metallic pigments that are typically present in a basecoatlayer. By “flop” is meant the visual change in brightness or lightnessof the metallic aluminum flake with a change in viewing angle, that is,a change of from 90 to 180 degrees. The greater the visual change fromlight to dark appearance, the better the flop. The flop accentuates thelines and curves of an automobile; therefore, it is very important inachieving the sought after appearance of the coating. Therefore, inorder to prevent or substantially reduce the strike-in rheology controlagent has been used.

Another problem associated with a basecoat containing metallic pigmentswhether applied as a single coat or part of multi-coat system is thepresence of mottled appearance, which results from lack control overflake orientation.

However, one of the problems associated with conventional methods, suchas those disclosed in U.S. Pat. No. 5,506,325 attempts to improverheology control to alleviate sag problems that adversely affect theflop of metallic paints. The invention discloses the use of non-gelledcopolymer mixed with silica. However, a need still exists to improve thestrike-in resistance along the improved coating composition properties,such as lowered VOC and reduced cure time.

STATEMENT OF THE INVENTION

The present invention is directed to a coating composition comprising:

a crosslinkable component comprising an acid functional acryliccopolymer polymerized from a monomer mixture comprising 2 percent to 12percent of one or more carboxylic acid group containing monomers,percentages based on total weight of the acid functional acryliccopolymer, and 0.2 percent to 2 percent of amorphous silica, percentagesbased on total weight of the crosslinkable component; and

a crosslinking component.

DETAILED DESCRIPTION OF THE INVENTION

As used herein:

“Two-pack coating composition” means a thermoset coating compositionhaving two components stored in separate containers. The containerscontaining the two components are typically sealed to increase theirshelf life. The components are mixed just prior to use to form a potmix, which has a limited pot life, typically ranging from a few minutes(15 minutes to 45 minutes) to a few hours (4 hours to 8 hours). The potmix is applied as a layer of a desired thickness on a substrate surface,such as an auto body. After application, the layer dries and cures atambient or elevated temperatures to form a coating on the substratesurface having desired coating properties, such as, high gloss,mar-resistance and resistance to environmental etching.

“Low VOC coating composition” means a coating composition that includesthe range of from 0.1 kilograms (1.0 pounds per gallon) to 0.72kilograms (6.0 pounds per gallon), preferably 0.3 kilograms (2.6 poundsper gallon) to 0.6 kilograms (5.0 pounds per gallon) and more preferably0.34 kilograms (2.8 pounds per gallon) to 0.53 kilograms (4.4 pounds pergallon) of the solvent per liter of the coating composition. All VOC'sdetermined under the procedure provided in ASTM D3960.

“High solids composition” means a coating composition having solidcomponent of above 30 percent, preferably in the range of from 35 to 90percent and more preferably in the range of from 40 to 80 percent, allin weight percentages based on the total weight of the composition.

“GPC weight average molecular weight” means a weight average molecularweight measured by utilizing gel permeation chromatography. A highperformance liquid chromatograph (HPLC) supplied by Hewlett-Packard,Palo Alto, Calif. was used. Unless stated otherwise, the liquid phaseused was tetrahydrofuran and the standard was polymethyl methacrylate orpolystyrene.

“Tg” (glass transition temperature) measured in ° C. determined by DSC(Differential Scanning Calorimetry).

“Polydispersity” means GPC weight average molecular weight divided byGPC number average molecular weight. The lower the polydispersity(closer to 1), the narrower will be the molecular weight distribution,which is desired.

“(Meth)acrylate” means acrylate and methacrylate.

“Polymer solids” means a polymer in its dry state.

“Crosslinkable component” means a component that includes a compound,polymer or copolymer having functional groups positioned in the backboneof the polymer, pendant from the backbone of the polymer, terminallypositioned on the backbone of the polymer, or a combination thereof.

“Crosslinking component” is a component that includes a compound,polymer or copolymer having groups positioned in the backbone of thepolymer, pendant from the backbone of the polymer, terminally positionedon the backbone of the polymer, or a combination thereof, wherein thesegroups are capable of crosslinking with the functional groups on thecrosslinkable component (during the curing step) to produce a coating inthe form of crosslinked structures.

In coating application, especially the automotive refinish or OEMapplication, a key driver is productivity, i.e., the ability of a layerof a coating composition to dry rapidly to a strike-in resistant statesuch that a subsequently coated layer, such as a layer form clearcoating composition does not adversely affect the underlying layer. Oncethe top layer is applied, the multi-coat system should then curesufficiently rapidly without adversely affecting uniformity of color andappearance. The present invention addresses the forgoing issues byutilizing a unique crosslinking technology and an additive. Thus, thepresent coating composition includes a crosslinkable and crosslinkingcomponent.

The crosslinkable component includes 2 weight percent to 25 weightpercent, preferably 3 weight percent to 20 weight percent, morepreferably 5 weight percent to 15 weight percent of one or more acidfunctional acrylic copolymers, all percentages being based on the totalweight of the crosslinkable component. If the composition containsexcess of the upper limit of the acid functional acrylic copolymer, theresulting composition tends to have higher than required applicationviscosity. If the composition contains less than the lower limit of theacid functional copolymer, the resultant coating would haveinsignificant strike-in properties for a multi-coat system or flakeorientation control in general.

The crosslinkable component includes an acid functional acryliccopolymer polymerized from a monomer mixture that includes 2 weightpercent to 12 weight percent, preferably 3 weight percent to 10 weightpercent, more preferably 4 weight percent to 6 weight percent of one ormore carboxylic acid group containing monomers, all percentages beingbased on the total weight of the acid functional acrylic copolymer. Ifthe amount of the carboxylic acid group containing monomer in themonomer mixture exceeds the upper limit, the coatings resulting fromsuch a coating composition would have unacceptable water sensitivity andif the amount is less than the lower limit, the resultant coating wouldhave insignificant strike-in properties for a multi-coat system or flakeorientation control in general.

The acid functional acrylic copolymer preferably has a GPC weightaverage molecular weight ranging from 8,000 to 100,000, preferably from10,000 to 50,000 and more preferably from 12,000 to 30,000. Thecopolymer preferably has a polydispersity ranging from 1.05 to 10.0,preferably ranging from 1.2 to 8 and more preferably ranging from 1.5 to5. The copolymer preferably has a Tg of ranging from about −5° C. to+100° C., preferably from about 0° C. to 80° C. and more preferably fromabout 10° C. to 60° C.

The carboxylic acid group containing monomers suitable for use in thepresent invention include (meth)acrylic acid, crotonic acid, oleic acid,cinnamic acid, glutaconic acid, muconic acid, undecylenic acid, itaconicacid, crotonic acid, fumaric acid, maleic acid, or a combinationthereof. (Meth)acrylic acid preferred. It is understood that applicantsalso contemplate providing the acid functional acrylic copolymer withcarboxylic acid groups by producing a copolymer polymerized from amonomer mixture that includes anhydrides of the aforementionedcarboxylic acids and then hydrolyzing such copolymers to provide theresulting copolymer with carboxylic acid groups. Maleic and itaconicanhydrides are preferred. Applicants further contemplate hydrolyzingsuch anhydrides in them monomer mixture before the polymerization of themonomer mixture into the acid functional acrylic copolymer.

It is believed, without reliance thereon, that the presence ofcarboxylic acid groups in the copolymer of the present invention appearsto increase viscosity of the resulting coating composition due tophysical network formed by the well-known hydrogen bonding of carboxylgroups. As a result, such increased viscosity, assists in strike-inproperties in multi-coat systems and flake orientation control ingeneral.

The monomer mixture suitable for use in the present invention includes 5percent to 40 percent, preferably 10 percent to 30 percent, all based ontotal weight of the acid functional acrylic copolymer of one or morefunctional (meth)acrylate monomers. It should be noted that if theamount of the functional (meth)acrylate monomers in the monomer mixtureexceeds the upper limit, the pot life of the resulting coatingcomposition is reduced and if less than the lower limit is used, itadversely affects the resulting coating properties, such as durability.The functional (meth)acrylate monomer is provided with one or morecrosslinkable groups selected from a primary hydroxyl, secondaryhydroxyl, or a combination thereof

Some of suitable hydroxyl containing (meth)acrylate monomers have thefollowing structure:

wherein R is H or methyl and X is a divalent moiety, which can besubstituted or unsubstituted C₁ to C₁₈ linear aliphatic moiety, orsubstituted or unsubstituted C₃ to C₁₈ branched or cyclic aliphaticmoiety. Some of the suitable substituents include nitrile, amide,halide, such as chloride, bromide, fluoride, acetyl, aceotoacetyl,hydroxyl, benzyl and aryl. Some specific hydroxyl containing(meth)acrylate monomers in the monomer mixture include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate,3-hydroxypropyl(meth)acrylate, and 4hydroxybutyl(meth)acrylate.

The monomer mixture can also include one or more non-functional(meth)acrylate monomers. As used here, non-functional groups are thosethat do not crosslink with a crosslinking component. Some of suitablenon-functional C₁ to C₂₀ alkyl(meth)acrylates includemethyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate,butyl(meth)acrylate, pentyl(meth)acrylate, hexyl(meth)acrylate,octyl(meth)acrylate, nonyl(meth)acrylate, isodecyl(meth)acrylate, andlauryl(meth)acrylate; branched alkyl monomers, such asisobutyl(meth)acrylate, t-butyl(meth)acrylate and2-ethylhexyl(meth)acrylate; and cyclic alkyl monomers, such ascyclohexyl(meth)acrylate, methylcyclohexyl(meth)acrylate,trimethylcyclohexyl(meth)acrylate, tertiarybutylcyclohexyl(meth)acrylateand isobornyl(meth)acrylate. Isobornyl(meth)acrylate and butyl acrylateare preferred.

The monomer mixture can also include one or more of other monomers forthe purpose of achieving the desired properties, such as hardness,appearance and mar resistance. Some of the other such monomers include,for example, styrene, α-methyl styrene, acrylonitrile andmethacrylonitrile. When included, preferably, the monomer mixtureincludes such monomers in the range of 5 percent to 30 percent, allpercentages being in weight percent based on the total weight of thepolymers solids. Styrene is preferred.

Any conventional bulk or solution polymerization process can be used toproduce the acid functional acrylic copolymer of the present invention.One of the suitable processes for producing the copolymer of the presentinvention includes free radically solution polymerizing theaforedescribed monomer mixture.

The polymerization of the monomer mixture can be initiated by addingconventional thermal initiators, such as azos exemplified by Vazo® 64supplied by DuPont Company, Wilmington, Del.; and peroxides, such ast-butyl peroxy acetate. The molecular weight of the resulting copolymercan be controlled by adjusting the reaction temperature, the choice andthe amount of the initiator used, as practiced by those skilled in theart.

The crosslinking component of the present invention includes one or morepolyisocyanates, melamines, or a combination thereof. Polyisocyanatesare preferred.

Typically, the polyisocyanate is provided with in the range of 2 to 10,preferably 2.5 to 8, more preferably 3 to 5 isocyanate functionalities.Generally, the ratio of equivalents of isocyanate functionalities on thepolyisocyanate per equivalent of all of the functional groups present inthe crosslinking component ranges from 0.5/1 to 3.0/1, preferably from0.7/1 to 1.8/1, more preferably from 0.8/1 to 1.3/1. Some suitablepolyisocyanates include aromatic, aliphatic, or cycloaliphaticpolyisocyanates, trifunctional polyisocyanates and isocyanate functionaladducts of a polyol and difunctional isocyanates. Some of the particularpolyisocyanates include diisocyanates, such as 1,6-hexamethylenediisocyanate, isophorone diisocyanate, 4,4′-biphenylene diisocyanate,toluene diisocyanate, biscyclohexyl diisocyanate, tetramethylene xylenediisocyanate, ethyl ethylene diisocyanate, 1-methyltrimethylenediisocyanate, 1,3-phenylene diisocyanate, 1,5-napthalene diisocyanate,bis-(4-isocyanatocyclohexyl)-methane and 4,4′-diisocyanatodiphenylether.

Some of the suitable trifunctional polyisocyanates includetriphenylmethane triisocyanate, 1,3,5-benzene triisocyanate, and2,4,6-toluene triisocyanate. Trimers of diisocyanate, such as the trimerof hexamethylene diisocyanate sold under the trademark Desmodur®N-3390by Bayer Corporation of Pittsburgh, Pa. and the trimer of isophoronediisocyanate are also suitable. Furthermore, trifunctional adducts oftriols and diisocyanates are also suitable. Trimers of diisocyanates arepreferred and trimers of isophorone and hexamethylene diisocyanates aremore preferred.

Typically, the coating composition can include 0.1 weight percent to 40weight percent, preferably, 15 weight percent to 35 weight percent, andmore preferably 20 weight percent to 30 weight percent of the melamine,wherein the percentages are based on total weight of composition solids.

Some of the suitable melamines include monomeric melamine, polymericmelamine-formaldehyde resin or a combination thereof. The monomericmelamines include low molecular weight melamines which contain, on anaverage, three or more methylol groups etherized with a C₁ to C₅monohydric alcohol such as methanol, n-butanol, or isobutanol pertriazine nucleus, and have an average degree of condensation up to about2 and preferably in the range of about 1.1 to about 1.8, and have aproportion of mononuclear species not less than about 50 percent byweight. By contrast the polymeric melamines have an average degree ofcondensation of more than 1.9. Some such suitable monomeric melaminesinclude alkylated melamines, such as methylated, butylated, isobutylatedmelamines and mixtures thereof. Many of these suitable monomericmelamines are supplied commercially. For example, Cytec Industries Inc.,West Patterson, N.J. supplies Cymel® 301 (degree of polymerization of1.5,95% methyl and 5% methylol), Cymel® 350 (degree of polymerization of1.6,84% methyl and 16% methylol), 303, 325, 327 and 370, which are allmonomeric melamines. Suitable polymeric melamines include high amino(partially alkylated, —N, —H) melamine known as Resimene® BMP5503(molecular weight 690, polydispersity of 1.98, 56% butyl, 44% amino),which is supplied by Solutia Inc., St. Louis, Mo., or Cymel®1158provided by Cytec Industries Inc., West Patterson, N.J. Cytec IndustriesInc. also supplies Cymel® 1130 @ 80 percent solids (degree ofpolymerization of 2.5), Cymel® 1133 (48% methyl, 4% methylol and 48%butyl), both of which are polymeric melamines.

If desired, including appropriate catalysts in the crosslinkablecomponent can accelerate the curing process of a potmix of the coatingcomposition.

When the crosslinking component includes polyisocyanate, thecrosslinkable component of the coating composition preferably includes acatalytically active amount of one or more catalysts for acceleratingthe curing process. Generally, catalytically active amount of thecatalyst in the coating composition ranges from about 0.001 percent toabout 5 percent, preferably ranges from 0.005 percent to 2 percent, morepreferably ranges from 0.01 percent to 1 percent, all in weight percentbased on the total weight of crosslinkable and crosslinking componentsolids. A wide variety of catalysts can be used, such as, tin compounds,including dibutyl tin dilaurate and dibutyl tin diacetate; tertiaryamines, such as, triethylenediamine. These catalysts can be used aloneor in conjunction with carboxylic acids, such as, acetic acid. One ofthe commercially available catalysts, sold under the trademark, Fastcat®4202 dibutyl tin dilaurate by Elf-Atochem North America, Inc.Philadelphia, Pa., is particularly suitable.

When the crosslinking component includes melamine, it also preferablyincludes a catalytically active amount of one or more acid catalysts tofurther enhance the crosslinking of the components on curing. Generally,catalytically active amount of the acid catalyst in the coatingcomposition ranges from about 0.1 percent to about 5 percent, preferablyranges from 0.1 percent to 2 percent, more preferably ranges from 0.5percent to 1.2 percent, all in weight percent based on the total weightof crosslinkable and crosslinking component solids. Some suitable acidcatalysts include aromatic sulfonic acids, such as dodecylbenzenesulfonic acid, para- toluenesulfonic acid and dinonylnaphthalenesulfonic acid, all of which are either unblocked or blocked with anamine, such as dimethyl oxazolidine and 2-amino-2-methyl-1-propanol,n,n-dimethylethanolamine or a combination thereof. Other acid catalyststhat can be used are strong acids, such as phosphoric acids, moreparticularly phenyl acid phosphate, which may be unblocked or blockedwith an amine.

The crosslinkable component of the coating composition can furtherinclude in the range of from 0.1 percent to 95 percent, preferably inthe range of from 10 percent to 90 percent, more preferably in the rangeof from 20 percent to 80 percent and most preferably in the range of 30percent to 70 percent, all based on the total weight of thecrosslinkable component of an acrylic polymer, a polyester or acombination thereof. Applicants have discovered that by adding one ormore the foregoing polymers to the crosslinkable component, the coatingcomposition resulting therefrom provides coating with improved sagresistance, and flow and leveling properties.

The acrylic polymer suitable for use in the present invention can have aGPC weight average molecular weight exceeding 2000, preferably in therange of from 3000 to 20,000, and more preferably in the range of 4000to 10,000. The Tg of the acrylic polymer varies in the range of from 0°C. to 100° C., preferably in the range of from 10° C. to 80° C.

The acrylic polymer suitable for use in the present invention can beconventionally polymerized from typical monomers, such asalkyl(meth)acrylates having alkyl carbon atoms in the range of from 1 to18, preferably in the range of from 1 to 12 and styrene and functionalmonomers, such as, hydroxyethyl acrylate and hydroxyethyl methacrylate.

The polyester suitable for use in the present invention can have a GPCweight average molecular weight exceeding 1500, preferably in the rangeof from 1500 to 100,000, more preferably in the range of 2000 to 50,000,still more preferably in the range of 2000 to 8000 and most preferablyin the range of from 2000 to 5000. The Tg of the polyester varies in therange of from −50° C. to +100° C., preferably in the range of from −20°C. to +50° C.

The polyester suitable for use in the present invention can beconventionally polymerized from suitable polyacids, includingcycloaliphatic polycarboxylic acids, and suitable polyols, which includepolyhydric alcohols.

Examples of suitable cycloaliphatic polycarboxylic acids aretetrahydrophthalic acid, hexahydrophthalic acid,1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic acid,endomethylenetetrahydrophthalic acid, tricyclodecanedicarboxylic acid,endoethylenehexahydrophthalic acid, camphoric acid,cyclohexanetetracarboxylic and cyclobutanetetracarboxylic acid. Thecycloaliphatic polycarboxylic acids can be used not only in their cisbut also in their trans form and as a mixture of both forms. Examples ofsuitable polycarboxylic acids, which, if desired, can be used togetherwith the cycloaliphatic polycarboxylic acids, are aromatic and aliphaticpolycarboxylic acids, such as, for example, phthalic acid, isophthalicacid, terephthalic acid, halogenophthalic acids, such as, tetrachloro-or tetrabromophthalic acid, adipic acid, glutaric acid, azelaic acid,sebacic acid, fumaric acid, maleic acid, trimellitic acid, andpyromellitic acid.

Suitable polyhydric alcohols include ethylene glycol, propanediols,butanediols, hexanediols, neopentylglycol, diethylene glycol,cyclohexanediol, cyclohexanedimethanol, trimethylpentanediol,ethylbutylpropanediol, ditrimethylolpropane, trimethylolethane,trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol,tris(hydroxyethyl)isocyanate, polyethylene glycol and polypropyleneglycol. If desired, monohydric alcohols, such as, for example, butanol,octanol, lauryl alcohol, ethoxylated or propoxylated phenols may also beincluded along with polyhydric alcohols. The details of polyestersuitable for use in the present invention are further provided in theU.S. Pat. No. 5,326,820, which is hereby incorporated herein byreference. One commercially available polyester, which is particularlypreferred, is SCD®-1040 polyester, which is supplied by Etna ProductInc., Chagrin Falls, Ohio.

The crosslinkable component can further include one or more reactiveoligomers, such as those reactive oligomers disclosed in U.S. Pat. No.6,221,494, which is incorporated herein by reference; and non-alicyclic(linear or aromatic) oligomers, if desired. Such non-alicyclic-oligomerscan be made by using non-alicyclic anhydrides, such as succinic orphthalic anhydrides, or mixtures thereof. Caprolactone oligomersdescribed in U.S. Pat. No. 5,286,782 incorporated herein by referencecan also be used.

The crosslinkable component of the coating composition can furtherinclude one or more modifying resins, which are also known asnon-aqueous dispersions (NADs). Such resins are sometimes used to adjustthe viscosity of the resulting coating composition. The amount ofmodifying resin that can be used typically ranges from 10 percent to 50percent, all percentages being based on the total weight ofcrosslinkable component solids. The weight average molecular weight ofthe modifying resin generally ranges from 20,000 to 100,000, preferablyranges from 25,000 to 80,000 and more preferably ranges from 30,000 to50,000.

The crosslinkable or crosslinking component of coating composition ofthe present invention, typically contains at least one organic solventwhich is typically selected from the group consisting of aromatichydrocarbons, such as, petroleum naphtha or xylenes; ketones, such as,methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone oracetone; esters, such as, butyl acetate or hexyl acetate; and glycolether esters, such as propylene glycol monomethyl ether acetate. Theamount of organic solvent added depends upon the desired solids level aswell as the desired amount of VOC of the composition. If desired, theorganic solvent may be added to both components of the binder. Highsolids and low VOC coating composition is preferred.

The crosslinkable component of the coating composition of the presentinvention typically contains 0.2 weight percent to 2.0 weight percent,preferably 0.3 weight percent to 1.4 weight percent and more preferably0.4 weight percent to 1.2 weight percent of amorphous silica, preferablyhydrophobic amorphous fumed silica. All percentages being in weightpercent based on the total weight of the crosslinkable component. Theapplicants unexpectedly discovered that a coating composition having theaforedescribed a copolymer and the silica in the aforedescribed weightpercentages improves the strike-in resistance of the coating resultingfrom the coating composition. The amorphous silica suitable for use inthe present invention include colloidal silica, which has beenpartially, or totally surface modified through the silanization ofhydroxyl groups on the silica particle, thereby rendering part or all ofthe silica particle surface hydrophobic. Examples of suitablehydrophobic silica include AEROSIL R972, AEROSIL R812 and AEROSIL R805,all commercially available from Degussa Corporation. Particularlypreferred fumed silica is available from Degussa Corporation as AEROSILR 812. Other commercially available silica include SIBELITE® M3000(Cristobalite), SIL-CO-SIL®, ground silica, MIN-U-SIL®, micronizedsilica, all supplied by U.S. Silica Company, Berkeley Springs, W.Va.

The silica can be dispersed in the copolymer by a milling process usingconventional equipment such as high-speed blade mixers, ball mills, orsand mills. Preferably, the silica is dispersed separately in theacrylic polymer described earlier and then the dispersion can be addedto the crosslinkable component of the coating composition.

The coating composition is preferably formulated as a two-pack coatingcomposition wherein the crosslinkable component is stored in separatecontainer from the crosslinking component, which are mixed to form a potmix just before use.

The coating composition is preferably formulated as an automotive OEMcomposition or as an automotive refinish composition. These compositionscan be applied as a basecoat or as a pigmented monocoat topcoat over asubstrate. These compositions require the presence of pigments.Typically, a pigment-to-binder ratio of 1.0/100 to 200/100 is useddepending on the color and type of pigment used. The pigments areformulated into mill bases by conventional procedures, such as,grinding, sand milling, and high speed mixing. Generally, the mill basecomprises pigment and a dispersant in an organic solvent. The mill baseis added in an appropriate amount to the coating composition with mixingto form a pigmented coating composition.

Any of the conventionally used organic and inorganic pigments, such as,white pigments, like, titanium dioxide, color pigments, metallic flakes,such as, aluminum flake, special effects pigments, such as, coated micaflakes, coated aluminum flakes and extender pigments can be used.

The coating composition can also include other conventional formulationadditives, such as, wetting agents, leveling and flow control agents,for example, Resiflow® S (polybutylacrylate), BYK® 320 and 325 (highmolecular weight polyacrylates), BYK® 347 (polyether-modified siloxane),defoamers, surfactants and emulsifiers to help stabilize thecomposition. Other additives that tend to improve mar resistance can beadded, such as, silsesquioxanes and other silicate-basedmicro-particles.

To improve weatherability of the clear finish of the coatingcomposition, about 0.1% to 5% by weight, based on the weight of thecomposition solids, of an ultraviolet light stabilizer or a combinationof ultraviolet light stabilizers and absorbers can be added. Thesestabilizers include ultraviolet light absorbers, screeners, quenchersand specific hindered amine light stabilizers. Also, about 0.1% to 5% byweight, based on the weight of the composition solids, of an antioxidantcan be also added. Most of the foregoing stabilizers are supplied byCiba Specialty Chemicals, Tarrytown, N.Y.

The coating composition of the present invention is preferablyformulated in the form of a two-pack coating composition. The presentinvention is particularly useful as a basecoat for outdoor articles,such as automobile and other vehicle body parts. A typical auto or truckbody is produced from a steel sheet or a plastic or a compositesubstrate. For example, the fenders may be of plastic or a composite andthe main portion of the body of steel. If steel is used, it is firsttreated with an inorganic rust-proofing compound, such as, zinc or ironphosphate, called an E-coat and then a primer coating is appliedgenerally by electrodeposition. Typically, these electrodepositionprimers are epoxy-modified resins crosslinked with a polyisocyanate andare applied by a cathodic electrodeposition process. Optionally, aprimer can be applied over the electrodeposited primer, usually byspraying, to provide better appearance and/or improved adhesion of abase coating or a mono coating to the primer.

The present invention is also directed to a process for producing amulti-coat system on a substrate. The process includes the followingprocess steps:

The cross-linkable component of the aforedescribed coating compositionof the present invention is mixed with the crosslinking component of thecoating composition to form a pot-mix. Generally, the crosslinkablecomponent and the crosslinking component are mixed just prior toapplication to form a pot mix. The mixing can take place though aconventional mixing nozzle or separately in a container.

A layer of the pot mix generally having a thickness in the range of 15micrometers to 200 micrometers is applied over a substrate, such as anautomotive body or an automotive body that has precoated with aconventional E-coat followed by a conventional primer, or a conventionalprimer. The foregoing application step can be conventionallyaccomplished by spraying, electrostatic spraying, commercially suppliedrobot spraying system, roller coating, dipping, flow coating or brushingthe pot mix over the substrate. The layer after application is flashed,i.e., exposed to air, to reduce the solvent content from the potmixlayer to produce a strike-in resistant layer. The time period of theflashing step ranges from 5 to 15 minutes. Then a layer of aconventional clearcoat composition having a thickness in the range of 15micrometers to 200 micrometers is conventionally applied by theapplication means described earlier over the strike-in resistant layerto form a multi-layer system on the substrate. Any suitable conventionalclear coating compositions can be used in the multi-coat system of thepresent invention. For example, suitable clearcoats for use over thebasecoat of this invention include solvent borne organosilane polymercontaining clear coating composition disclosed U.S. Pat. No. 5,244,696;solvent borne polyisocyanate crosslinked clear coating composition,disclosed in U.S. Pat. No. 6,433,085; clear thermosetting compositionscontaining epoxy-functional polymers disclosed in U.S. Pat. No.6,485,788; wherein all of the forgoing patents are hereby incorporatedherein by reference.

The multi-layer system is then cured into said multi-coat system underambient conditions, at elevated temperatures, or under ambientconditions followed by elevated temperatures. The cure temperature canrange from ambient to 204° C. Under typical automotive OEM applications,the multi-layer system can be typically cured at elevated temperaturesranging from 60° C. to 160° C. in about 10 to 60 minutes. Preferably,for automotive refinish applications curing can take place at aboutambient to 60° C., and for heavy-duty truck body applications it cantake place at about 60° C. to 80° C. The cure under ambient conditionsoccurs in about 30 minutes to 24 hours, generally in about 30 minutes to4 hours to form a coating on the substrate having the desired coatingproperties. It is further understood that the actual curing time candepend upon the thickness of the applied layer, the cure temperature,humidity and on any additional mechanical aids, such as fans, thatassist in continuously flowing air over the coated substrate toaccelerate the cure rate. It is understood that actual curingtemperature would vary depending upon the catalyst and the amountthereof, thickness of the layer being cured and the amount of thecrosslinking component utilized. For example, the curing step can beaccelerating by adding a catalytically active amount of a catalyst oracid catalyst to the composition.

It should be noted that if desired the present invention also includes amethod of applying a layer of the aforedescribed pot mix, which is thencured to produce a coating, such as a basecoat, on a substrate that mayor may not include other previously applied coatings, such as an E-coator a primer coat.

The suitable substrates for applying the coating composition of thepresent invention include automobile bodies, any and all itemsmanufactured and painted by automobile sub-suppliers, frame rails,commercial trucks and truck bodies, including but not limited tobeverage bodies, utility bodies, ready mix concrete delivery vehiclebodies, waste hauling vehicle bodies, and fire and emergency vehiclebodies, as well as any potential attachments or components to such truckbodies, buses, farm and construction equipment, truck caps and covers,commercial trailers, consumer trailers, recreational vehicles, includingbut not limited to, motor homes, campers, conversion vans, vans,pleasure vehicles, pleasure craft snow mobiles, all terrain vehicles,personal watercraft, motorcycles, boats, and aircraft. The substratefurther includes industrial and commercial new construction andmaintenance thereof; cement and wood floors; leather; walls ofcommercial and residential structures, such office buildings and homes;amusement park equipment; concrete surfaces, such as parking lots anddrive ways; asphalt and concrete road surface, wood substrates, marinesurfaces; outdoor structures, such as bridges, towers; coil coating;railroad cars; printed circuit boards; machinery; OEM tools; signage;fiberglass structures; sporting goods; and sporting equipment.

EXAMPLES

Test Procedures

BK Dry Time

Surface drying times of coated panels measured according to ASTM D5895.

Viscosity Measurement

The viscosity of the pot mix (mixture of all of the components of thecoating composition) of the coating compositions was measured by usingthe conventional Zahn #3 cup supplied by VWR Scientific ProductsCorporation. The viscosity was measured as soon as the pot mix wasprepared. The reading was recorded as number of seconds it took for thepot mix to drain from the Zahn #3 cup [ASTM D1084 (Method D)].

Gloss Measurement

Gloss was measured at 20° using a Byk-Gardener Glossmeter.

Distinctness of Image (DOI)

DOI was measured using a Hunterlab Model RS 232 (HunterLab, Reston,Va.).

EXAMPLES Acid Functional Acrylic Copolymer 1 (Sty/BA/IBOA/HPMA/HEMA/MAA:20.0/40.0/20.0/7.5/7.5/5.0% by weight)

A 12-liter flask was equipped with a thermometer, stirrer, funnels,heating mantle, reflux condenser and a means for maintaining a nitrogenblanket over the reactants. The flask was held under nitrogen positivepressure and the following ingredients were charged to the flask in theorder shown in Table 1 and in through a procedure described below: TABLE1 Weight (gram) Portion 1 Methyl amyl ketone 649.6 Portion 2 Styrene(Sty) 473.8 Butyl acrylate (BA) 947.6 Methacrylic acid (MAA) 118.4Isobornyl acrylate (IBOA) 473.8 Hydroxypropyl methacrylate (HPMA) 177.72-Hydroxyethyl methacrylate (HEMA) 177.7 Portion 3 Methyl amyl ketone38.5 Portion 4 Initiator* 13.0 Methyl amyl ketone 384.9 Portion 5 Methylamyl ketone 28.9 Portion 6 Methyl amyl ketone 116.1 Total 3600.0*Di-t-butyl peroxide supplied by Elf Atochem North America, Inc.,Philadelphia, Pennsylvania.

Portion 1 was charged to the flask and heated to reflux temperature.Portion 2 was fed to the reactor over 195 minutes while Portion 3 wassimultaneously fed to the reactor over 200 minutes. The reaction mixturewas held at reflux temperature throughout the course of the additions.Portion 4 was then added as a rinse for Portion 2 at the end of thefeed, and Portion 5 was added as a rinse for Portion 3. Reflux wascontinued for another 2 hours. Portion 6 was added and the solution wascooled to room temperature and filled out. The resulting polymersolution was clear and had a solid content of about 65.7% and aGardner-Holt viscosity of Z1. The polymer had a GPC Mw of 21,499 and GPCMn of 5,800 based on GPC using polystyrene as the standard and a Tg of25.6° C. as measured by DSC.

Acid Functional Acrylic Copolymer 2 (Sty/BA/EHA/IBOA/HPMA/HEMA/MAA:15.0/30.0/20.0/15.0/7.5/7.5/5.0% by weight)

The following ingredients were charged to the flask in the order shownin Table 2 and in through a procedure described above in Example 1:TABLE 2 Weight (gram) Portion 1 Methyl amyl ketone 649.6 Portion 2Styrene (Sty) 355.3 Butyl acrylate (BA) 710.7 Methacrylic acid (MAA)118.4 2-Ethylhexyl acrylate (EHA) 473.8 Isobornyl acrylate (IBOA) 355.3Hydroxypropyl methacrylate (HPMA) 177.7 2-Hydroxyethyl methacrylate(HEMA) 177.7 Portion 3 Methyl amyl ketone 38.5 Portion 4 Initiator* 13.0Methyl amyl ketone 384.9 Portion 5 Methyl amyl ketone 28.9 Portion 6Methyl amyl ketone 116.1 Total 3600.0*Di-t-butyl peroxide supplied by Elf Atochem North America, Inc.,Philadelphia, Pennsylvania.

The resulting polymer solution was clear and had a solid content ofabout 65.5% and a Gardner-Holt viscosity of W−½. The polymer had a GPCMw of 15,049 and GPC Mn of 4,789 based on GPC using polystyrene as thestandard and a Tg of +3.7° C. as measured by DSC.

Acid Functional Acrylic Copolymer 3 (Sty/BA/IBOA/HPMA/HEMA/MAA:29.0/31.0/20.0/7.5/.75/5.0% by weight)

The following ingredients were charged to the flask in the order shownin Table 3 and in through a procedure described above in Example 1:TABLE 3 Weight (gram) Portion 1 Methyl amyl ketone 1243.0 Portion 2Styrene (Sty) 1314.7 Butyl acrylate (BA) 1405.3 Methacrylic acid (MAA)226.7 Isobornyl acrylate (IBOA) 906.8 Hydroxypropyl methacrylate (HPMA)339.9 2-Hydroxyethyl methacrylate (HEMA) 339.9 Portion 3 Methyl amylketone 73.7 Portion 4 Initiator* 24.9 Methyl amyl ketone 736.6 Portion 5Methyl amyl ketone 55.2 Portion 6 Methyl amyl ketone 533.3 Total 7200*Di-t-butyl peroxide supplied by Elf Atochem North America, Inc.,Philadelphia, Pennsylvania.

The resulting polymer solution was clear and had a solid content ofabout 64.4% and a Gardner-Holt viscosity of Y+½. The polymer had a GPCMw of 24,601 and GPC Mn of 7,087 based on GPC using polystyrene as thestandard and a Tg of +44.3° C. as measured by DSC.

Low Mw Acrylic Dispersion Polymer for Pigment(Sty/MMA/EHA/HEMA/IBOMA/BMA: 10/10/15/30/10/25% by weight)

A 12-liter flask was equipped with a thermometer, stirrer, funnels,heating mantle, reflux condenser and a means for maintaining a nitrogenblanket over the reactants. The flask was held under nitrogen positivepressure and the following ingredients were charged to the flask in theorder shown in Table 4 and in through a procedure described below: TABLE4 Weight (gram) Portion 1 Butyl acetate 1489.83 Portion 2 Styrene (Sty)447.95 Methyl methacrylate (MMA) 1119.86 2-Ethyihexyl acrylate (EHA)671.92 2-Hydroxyethyl methacrylate (HEMA) 1343.84 Isobornyl methacrylate(IBOMA) 447.95 Butyl methacrylate (BMA) 447.95 Portion 3 Intiator*418.08 Butyl acetate 725.56 Portion 4 Butyl acetate 87.07 Total 7200.01*Lupersol ® 70 t-butyl peroxyacetate (75%) supplied by Elf Atochem NorthAmerica, Inc., Philadelphia, Pennsylvania.

Portion 1 was charged to the flask and heated to reflux temperature.Portion 2 and 90% of the Portion 3 were simultaneously fed to thereactor over 300 minutes. The reaction mixture was held at refluxtemperature throughout the course of the additions. The reaction mixturewas refluxed for 30 minutes, and then the remaining 10% of the Portion 3was fed to the reactor over 30 minutes. At the end of the feed, Portion4 was used to rinse the feed line. Reflux was continued for another 2hours. The polymer solution was cooled to room temperature and filledout. The resulting polymer solution was clear and had a solid content ofabout 66.6% and a Gardner-Holt viscosity of Y. The polymer had a GPC Mwof 5,591 and a GPC Mn of 2,985 based on GPC using polystyrene as thestandard.

Low Mw Dispersion Polyester (NPG/TMP/HDPA/AA: 41.51/8.98/25.41/24.09% byweight)

A 12-liter flask was equipped with a thermometer, stirrer, funnels,heating mantle, reflux condenser and a means for maintaining a nitrogenblanket over the reactants. The flask was held under nitrogen positivepressure and the following ingredients were charged to the flask in theorder shown in Table 5 and in through a procedure described below: TABLE5 Weight (gram) Portion 1 Deionized water 452.70 Neopentyl gylcol (NPG)4074.30 Monobutyl tin oxide 5.40 Portion 2 Trimethylol propane (TMP)881.60 Hexahydrophthalic anhydride (HDPA) 2494.10 Adipic acid (AA)2364.30 Aromatic hydrocarbon* 371.80 Portion 3 Ethyl acetate 846.00Portion 4 Ethyl acetate 358.10 Total 11848.30*154-174C distillation cut supplied by ExxonMobil Chemical Co., Huston,Texas.

Portion 1 was charged in order to the flask and heated to 70° C. to meltthe mixture. Portion 2 was charged in order with mixing. The mixture washeated to distill water without exceeding the temperature of 240° C.until the acid number of 3.0-7.0 was reached. The flask content werecooled and diluted with Portion 3. The Portion 4 was used to adjust thesolids and viscosity to the desired range. The resulting polymersolution was clear and had a solid content of 85.6% and a Gardner-Holtzviscosity of Z+½. The polymer had a GPC Mw of 2,210 and a GPC Mn of1,058 based on GPC using polystyrene as the standard.

Silica Dispersion Example

TABLE 6 Ingredient Weight (gram) Portion 1 Low MW acrylic copolymer10,976 Methyl amyl ketone 9,296 Isopropanol 5,208 Portion 2 Amorphoussilica powder 2,520 Total 28,000

The Portion 1 was mixed for 15 minutes. The silica powder was slowlyadded with mixing for a smooth incorporation over 1 hour. The mixturewas then passed through a sand mill that was loaded with 0.8 mm glassbeads at a rate of 125 seconds per pint.

Paint Example Set 1

The ingredients were mixed well to make a crosslinkable component for ablue metallic topcoat coating composition. TABLE 7 Weight (gram) Comp.Comp. Comp. Ingredient Ex. 1 Ex. 2 Ex 3 Ex. 1 Ex. 2 Ex. 3 Silica 0.024.5 11.1 11.1 11.1 11.1 dispersion Low MW 8.5 3.9 3.9 3.9 3.9 polyolAcid functional 15.9 acrylic copolymer 1 Acid functional 15.9 acryliccopolymer 2 Acid functional 15.9 15.9 4.3 15.9 acrylic copolymer 3 LowMV 32.6 12.7 32.3 23.5 23.5 23.5 polyester 513H¹. 2.2 2.1 2.1 2.1 2.12.1 522H¹. 5.0 4.7 4.9 4.8 4.8 4.8 504H¹. 6.6 6.2 6.5 6.4 6.4 6.4 507H¹.21.4 20.3 21.0 20.9 20.9 20.9 Dibutyl tin 0.01 0.01 0.01 0.01 0.01 0.01dilaurate Heptane 0.8 1.2 0.9 0.9 0.9 09 Ethyl acetate 1.7 1.3 1.5 1.61.6 1.6 8685S². 13.8 2.6 11.5 8.9 8.9 8.9 Total 100.0 100.0 100.0 100.0100.0 100.0¹DuPont Master Tint, high solids mixing color for OEM/Fleet paintproduct, Wilmington, DE.²DuPont Imron ® 5000 reducer, Wilmington DE.

The resulting crosslinkable component had the following characteristics.TABLE 8 Comp. Comp. Comp. Ex. 1 Ex. 2 Ex 3 Ex. 1 Ex. 2 Ex.3 % Silica¹0.0 2.2 1.0 1.0 1.0 1.0 % Acid functional 10 10 2.7 10 10 10 acryliccopolymer¹. Viscosity (cps)². 315 1205 455 615 405 420 Viscosity(sec.)³. 13.7 23.2 12.6 15.4 11.3 13.5 Viscosity (sec.)⁴. 14 14.6 11.214 12 10.5 Viscosity (sec.)⁵. 23.4 23.5 14.2 21.8 17.4 16.4¹All percentages are based on the total weight of the crosslinkablecomponent.²Measured by Brookfield viscometer at 20 rpm using a #2 spindle.³Measured by a Zahn 3 cup.⁴Measured by a Zahn 3 cup after the crosslinkable component was mixedwith the crosslinking component and the paint is ready to spray.⁵Measured by a Zahn 3 cup one hour after the crosslinkable component wasmixed with the crosslinking component.

The crosslinkable component was mixed with a polyisocyanate basedcrosslinking component, DuPont Imron® 194S, in a volume ratio of 3:1.The resulting coating composition was immediately sprayed onto analuminum panel until the film thickness of the paint is high enough tohide the standard black and white hiding sticker commonly used in theindustry. The panel was air dried for about 15 minutes before it wasplaced vertically in an oven and cured at 82° C. (180° F.) for 30minutes to produce a blue metallic colored topcoat. TABLE 9 Comp. Comp.Comp. Ex. 1 Ex. 2 Ex 3 Ex. 1 Ex. 2 Ex. 3 Film thickness 2.2-2.4 2.1-2.42.1-2.4 2.0-2.4 2.9-3.3 2.3-2.6 (mil) 20 gloss 78 78 76 76 79 79 60gloss 90 91 89 89 89 90 DOI 76 62 70 75 81 83 Appearance 6.7 2.7 6.3 6.16.2 6.0 rating1. All percentages are based on the total weight of the crosslinkablecomponent.2. Measured by Brookfield viscometer at 20 rpm using a #2 spindle.3. Measured by a Zahn 3 cup

Comparative Example 1 showed a slight tendency to sag. ComparativeExample 2 had a high viscosity, which adversely affected the sprayingproperties, and poor flow properties. The resulting panel had aorange-peel like uneven appearance and a low DOI. Comparative Example 3showed a blotchy or mottled appearance. The three examples of thisinvention had nice spraying properties and the resulting panels showedimproved appearance.

1. A process for producing a multi-coat system on a substratecomprising: (a) mixing a cross-linkable component of a coatingcomposition with a crosslinking component of said coating composition toform a pot-mix, said crosslinkable component comprising an acidfunctional acrylic copolymer polymerized from a monomer mixturecomprising 2 weight percent to 12 weight percent of carboxylic acidgroup containing monomer based on total weight of the acid functionalacrylic copolymer, and 0.2 weight percent to 2 weight percent ofamorphous silica based on total weight of the crosslinkable component;(b) applying a layer of said pot-mix over said substrate; (c) flashingsaid layer of said pot-mix into a strike-in resistant layer; (d)applying a layer of a clearcoat composition over said strike-inresistant layer to form a multi-layer system on said substrate; and (e)curing said multi-layer system into said multi-coat system.
 2. Theprocess of claim 1 wherein a time period of said flashing step rangesfrom 5 to 15 minutes.
 3. The process of claim 1 wherein said curing steptakes place under ambient conditions, at elevated temperatures, or underambient conditions followed by elevated temperatures.
 4. The process ofclaim 1 or 3 elevated temperatures.
 5. The process of claim 1 furthercomprising producing a primer coat on said substrate before said step(b).
 6. The process of claim 1 further comprising producing an E-coatfollowed by a primer coat on said substrate with before said step (b).7. The process of claim 1 wherein said acid functional acrylic copolymerhas a GPC weight average molecular weight ranging from 8,000 to 100,000and a polydispersity ranging from 1.05 to 10.0.
 8. The process of claim1 wherein said acid functional acrylic copolymer has Tg ranging from −5°C. to +100° C.
 9. The process of claim 1 wherein said monomer mixturecomprises one or more functional (meth)acrylate monomers and one or morenon-functional (meth)acrylate monomers.
 10. The process of claim 7wherein said monomer mixture comprises 5 percent to 40 percent based ontotal weight of the acid functional acrylic copolymer of said functional(meth)acrylate monomers.
 11. The process of claim 8 wherein saidfunctional (meth)acrylate monomer is provided with one or morecrosslinkable groups selected from the group consisting of a primaryhydroxyl, secondary hydroxyl and a combination thereof.
 12. The processof claim 1 wherein said crosslinking component comprises apolyisocyanate, melamine or a combination thereof.
 13. The process ofclaim 11 wherein a ratio of equivalents of isocyanate functionalities onsaid polyisocyanate per equivalents of the functional groups on saidacid functional acrylic copolymer ranges from 0.5/1 to 3.0/1.
 14. Theprocess of claim 11 comprising 0.1 weight percent to 40 weight percentof said melamine, wherein said percentages are based on total weight ofcomposition solids.
 15. The process of claim 11 further comprisingaccelerating said (d) step by adding a catalytically active amount of acatalyst to said composition.
 16. The process of claim 14 furthercomprising accelerating said (d) step by adding a catalytically activeamount of an acid catalyst to said composition.
 17. The process of claim1 wherein said coating composition comprises pigment.
 18. The process ofclaim 1 formulated as an automotive OEM composition.
 19. The process ofclaim 1 formulated as an automotive refinish composition.
 20. Theprocess of claim 1, 17, 18 or 19 wherein said substrate is an automotivebody.
 21. The process of claim wherein said composition is formulated asa low VOC coating composition comprising a solvent ranging of from 0.1kilograms (1.0 pounds per gallon) to 0.72 kilograms (6.0 pounds pergallon) per liter of said composition.